Bulletin of the Polish Academy of Sciences: Technical Sciences

The Bulletin of the Polish Academy of Sciences: Technical Sciences
is published bimonthly by the Division IV Engineering Sciences of the
Polish Academy of Sciences, since the beginning of the existence of the
PAS in 1952. The journal is peer‐reviewed and is published both in
printed and electronic form. It is established for the publication of
original high quality papers from multidisciplinary Engineering sciences
with the following topics preferred:

Abstrakt

Traditional fluid mechanics edifies the indifference between liquid and
gas flows as long as certain similarity parameters  most prominently
the Reynolds number  are matched. This may or may not be the case for
flows in nano- or microdevices. The customary continuum, Navier-Stokes
modelling is ordinarily applicable for both air and water flowing in
macrodevices. Even for common fluids such as air or water, such
modelling bound to fail at sufficiently small scales, but the onset for
such failure is different for the two forms of matter. Moreover, when
the no-slip, quasi-equilibrium Navier  Stokes system is no longer
applicable, the alternative modelling schemes are different for gases
and liquids. For dilute gases, statistical methods are applied and the
Boltzmann equation is the cornerstone of such approaches. For liquid
flows, the dense nature of the matter precludes the use of the kinetic
theory of gases, and numerically intensive molecular dynamics
simulations are the only alternative rooted in first principles. The
present article discusses the above issues, emphasizing the differences
between liquid and gas transport at the microscale and the physical
phenomena unique to liquid flows in minute devices.

Abstrakt

A review is given on a number of colloidal phenomena with special
reference to their applicability to nanoparticles. Phenomena addressed
include preparation, electric double layers and their characterization,
electrokinetics, van der Waals and Lifshits forces, electric and steric
particle interaction.

Abstrakt

In this paper we present the numerical simulation-based design of a new
microfluidic device concept for electrophoretic mobility and (relative)
concentration measurements of dilute mixtures. The device enables
stationary focusing points for each species, where the locally applied
pressure driven flow (PDF) counter balances the species electrokinetic
velocity. The axial location of the focusing point, along with the PDF
flowrate and applied electric field reveals the electrokinetic mobility
of each species. Simultaneous measurement of the electroosmotic mobility
of an electrically neutral specie can be utilized to calculate the
electrophoretic mobility of charged species. The proposed device
utilizes constant sample feeding, and results in time-steady
measurements. Hence, the results are independent of the initial sample
distribution and flow dynamics. In addition, the results are insensitive
to the species diffusion for large Peclet number flows (Pe > 400),
enabling relative concentration measurement of each specie in the dilute
mixture.

Abstrakt

We discuss recent progress in hybrid atomistic-continuum methods with
particular emphasis on developments in boundary condition imposition in
molecular simulations, an essential ingredient of hybrid methods. Both
Dirichlet (state variable) and flux boundary conditions are discussed.
We also briefly review various coupling approaches and discuss the
effects of compressibility and molecular fluctuations on the choice of
coupling method. Common elements between hybrid methods and related
multiscale simulation approaches are also briefly discussed.

Abstrakt

The topic of incompressible fluid flow in rough channels is of practical
interest in many diverse applications. It also forms the basis of our
understanding of fluid-wall interactions, turbulent eddy generation, and
their effect on the frictional pressure losses. Although this topic is
also of fundamental interest, the work in this area is entirely guided
by the experimental work of earlier investigators [16]. The works by
Nikuradse [4] and Colebrook [5] constitute a major milestone from which
useful empirical models are derived. As we approach the microscale,
Nikuradses experimental work again is brought to focus, perhaps this
time to gain an insight into the mechanisms affecting fluid-wall
interaction in rough channels. In this paper, Nikuradses work is
revisited in light of the recent experimental work on roughness effects
in microscale flow geometries.

Abstrakt

The paper presents the results of a numerical study devoted to the
hydraulic properties of a network of parallel triangular microchannels
(hydraulic diameter Dh = 110 um). Previous experimental investigations
had revealed that pressure drop through the microchannels system
dramatically increases for the Reynolds number exceeding value of 10.
The disagreement of the experimental findings with the estimations of
flow resistance based on the assumption of fully developed flow were
suspected to result from the so-called scale effect. Numerical
simulations were performed by using the classical system of flow
equations (continuity and Navier-Stokes equations) in order to explain
the observed discrepancies. The calculations showed a very good
agreement with the experimental results proving that there is no scale
effect for the microchannels considered, i.e. the relevance of the
constitutive flow model applied was confirmed. It was also clearly
indicated that the excessive pressure losses in the high Reynolds number
range are due to the secondary flows and separations appearing in
several regions of the microchannel system.

Abstrakt

This mini-review reports the recent advances in the hydrodynamic
techniques for formation of bubbles of gas in liquid in microfluidic
systems. Systems comprising ducts that have widths of the order of 100
micrometers produce suspensions of bubbles with narrow size
distributions. Certain of these systems have the ability to tune the
volume fraction of the gaseous phase  over the whole range from zero to
one. The rate of flow of the liquids through the devices determines the
mechanism of formation of the bubbles  from break-up controlled by the
rate of flow of the liquid (at low capillary numbers, and in the
presence of strong confinement by the walls of the microchannels), to
dynamics dominated by inertial effects (at high Weber numbers). The
region of transition between these two regimes exhibits nonlinear
behaviours, with period doubling cascades and irregular bubbling as
prominent examples. Microfluidic systems provide new and uniquely
controlled methods for generation of bubbles, and offer potential
applications in micro-flow chemical processing, synthesis of materials,
and fluidic optics.

Abstrakt

A systematic approach for analyzing the static and dynamic
electromechanical response of electrostatic actuators is presented. The
analysis is based on energy methods. An analysis approach for extracting
dynamic response parameters of electrostatic actuators, while only
considering static states of the system, is presented. This is an
efficient method for extracting the dynamic pull-in parameters because
it does not require time integration of momentum equations.

Abstrakt

Very thin liquid jets can be obtained using electric field, whereas an
electrically-driven bending instability occurs that enormously increases
the jet path and effectively leads to its thinning by very large ratios,
enabling the production of nanometre size fibres. This mechanism,
although it was discovered almost one century ago, is not yet fully
understood. In the following study, experimental data are collected,
with the dual goal of characterizing the electro-spinning of different
liquids and evaluating the pertinence of a theoretical model.

Abstrakt

Dissipative Particle Dynamics (DPD) is a simulation method at mesoscopic
scales that bridges the gap between molecular dynamics and continuum
hydrodynamics. It can simulate efficiently complex liquids and dense
suspensions using only a few thousands of virtual particles and at
speed-up factors of more than one hundred thousands compared to
Molecular Dynamics. Lowes approach provides a powerful alternative to
the usual DPD integrating schemes. Here, we demonstrate the details and
potential of Lowes scheme. We compute viscosity, diffusivity and
Schmidt number values and we present comparison of wormlike chain models
under shear with experimental and Brownian Dynamics results for ll-phage
DNA.

Abstrakt

Molecular motors are natures nanomachines, and are the essential agents
of movement that are an integral part of many living organisms. The
supramolecular machine, called the nuclear pore complex (NPC), controls
the transport of all cellular material between the cytoplasm and the
nucleus that occurs naturally in all biological cells. In the presence
of appropriate chemical stimuli, the NPC opens or closes, like a gating
mechanism, and permits the flow of material into and out of the nucleus.
As a first step in understanding the design characteristics of the NPC,
nanoscale studies were conducted to understand the transport
characteristics of an idealized NPC model using CFD analysis, discrete
element transport and coupled fluid-solid analysis. Results of pressure
and velocity profiles obtained from the models indicate that the fluid
density, flexibility of walls and the geometry of the flow passage are
important in the design of NPC based nano- and micro-motors.

Abstrakt

The paper gives an introduction to nanostructuring techniques used for
industrial fabrication of bulk nanocrystalline metals  basic

materials utilized in shaping nanoscale structures. Nanostructured
metals, called nanometals, can be produced by severe plastic deformation
(SPD). We give an expert coverage of current achievements in all
important SPD methods and present future industry developments and
research directions including both batch and continuous processes. In
the laboratories of both WUT and UOS we have developed industry standard
equipment and machinery for nanometals processing. Utilizing the latest
examples from our research, we provide a concise introduction to the
field of mass production of nanometals for nanotechnology.

Abstrakt

A short literature survey which justifies coating of ceramic cutting
inserts is presented. The results reported are on selected nitride

coatings, in particular nanoscale multilayer, with layers of type
Ti-Zr-N, TiN, ZrN and (TiAl)N, deposited by the arc PVD method on
oxidecarbide ceramic cutting inserts of type TACN and TW2 produced at
the Institute of Advanced Manufacturing Technology. Measurements and
quality assessments were made, including of thickness of the coatings
and of their constituent micro and nanolayers, microhardness of the
coating and of the substrate, surface roughness of the inserts and of
the cylindrical workpieces turned with these tools. Lifetimes of the
coated and uncoated inserts were compared in turning an alloy tool
steel. A significant increase in lifetime of the coated TW2 cutting
tools was shown.

Abstrakt

The techniques of micro and nano structurization of surfaces of various
materials are utilized in electronics and medicine. Such procedure as
wet and dry etching allows to fabricate protruded or recessed micro and
nanostructures on the surface. In the paper some examples of utilization
of a surface structurization, known from literature, are described. Some
structurization methods and experimental results for fabrication of the
arrays of sharp microtips are presented. Wet and/or dry etching, and
thermal oxidation process were used to form the arrays of sharp gated
and non-gated, protruded or recessed silicon microtips on silicon wafer.
For the first time, the arrays of silicon carbide (SiC) microtips on
glass wafer have been produced by use of the transfer mold technique.
Arrays of sharp microtips are used as field electron emission cathodes
for vacuum microelectronics devices. Some electron emission measurements
for these cathodes have been carried out. New application of silicon
microtips array in biochemistry has been tested with satisfactory
results.

Polityka Open Access

Bulletin of the Polish Academy of Sciences: Technical Sciences is an open access journal with all content available with no charge in full text version. The journal content is available under the licencse CC BY-NC-ND 4.0.